The transmission unit of a mobile phone, a wireless LAN (Local Area Network) communication device, or the like is required to operate with lower power consumption while ensuring the accuracy of transmission signals irrespective of the magnitude of its output power. In particular, a power amplifier circuit disposed in the last stage of the transmission unit of a communication device is required to have high power efficiency because it consumes at least 50% of the overall power consumption of the communication device.
Recently, switching amplifier circuits are receiving attention as power amplifier circuits that are expected to have high power efficiency. The switching amplifier circuit operates on the assumption that an input signal is a signal having a pulse waveform, and amplifies power while maintaining the waveform. After frequency components other than a desired frequency component are suppressed by a filter element, the pulse-waveform signal amplified by the switching amplifier circuit is emitted in the air from an antenna.
Each of Patent Literature 1 and Non-patent Literature 1 discloses a configuration of a transmitter including a D-class amplifier circuit, which is a type of switching amplifier circuit. This transmitter reproduces an RF-radio signal by amplifying an RF-pulse signal generated by a RF-signal generator by using a driver amplifier and the D-class amplifier circuit and removing unnecessary components of the amplified RF-pulse signal by using a filter disposed behind the D-class amplifier circuit.